Optimal Time for Cardio (duration)


GOAL:  Fat Loss

Is there an optimal amount of time for cardio after which the calorie burning aspect diminishes? I have heard that you have to do cardio for at least 20 minutes, but is there a maximum time after which the benefits decrease? Would it be better for me to run for an hour 3 times a week or for a half hour 6 times a week??

Answered By:

Mike Behnken, MS, CSCS ANswers the Fitness Question


The Optimal time for Cardio Depends on your Goals

Accomplishing your goal of fat loss is far more complex than the simple question of whether to do cardio for an hour 3 times a week or for a half hour 6 times a week.

Since the ultimate determinant of fat loss is whether you burn more calories than you consume you have to consider your caloric intake, BMR and activity levels to figure out what the optimal time for cardio is for you.

Long Duration equals low intensity and vice versaIf you work a desk job and watch TV in your spare time with little or no physical activity other than your 3 days of running, it would be better to run 6 times per week for half an hour, because your intensity for the running will be greater which will lead to more burned calories during rest.

If you have an active lifestyle, 3 60 minute, low intensity runs would be just fine because you burn extra calories throughout the day with other activities.

Running always burns the same amount of calories (energy) at the same intensity regardless of the point in training.

The longer you train, the more fat is used for energy but this does not mean that long duration exercise is best for fat burning considering you are talking 3 hours of running vs. 165 hours of not running over the course of a week.

What you want to avoid is exercise which lasts very long (over 60 minutes) because your body may begin using protein as fuel which will run you down, and slow down your metabolism.

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